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They found in the 30 minutes after smoking the e-cigarettes containing nicotine, there was a significant increase in blood pressure, heart rate and arterial stiffness.

There was no such effect in the volunteers who smoked the e-cigarettes without nicotine.

Young woman smoking electronic cigarette

Dr Magnus Lundback, of the Danderyd University Hospital, Karolinska Institute, said: "The number of e-cigarette users has increased dramatically in the last few years. E-cigarettes are regarded by the general public as almost harmless.

"The e-cigarette industry markets their product as a way to reduce harm and to help people to stop smoking tobacco cigarettes.

"However, the safety of e-cigarettes is debated, and a growing body of evidence is suggesting several adverse health effects.